Increment the repeated value in xslt inside for-each - xslt

Question

Here I want to count/Increment the repeated emp_no using for each.
and I just want to concatenate emp_no with duplicate no count..
Here is my XSLT style sheet.
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:map="http://www.w3.org/2005/xpath-functions/map"
xmlns:array="http://www.w3.org/2005/xpath-functions/array" exclude-result-prefixes="#all"
version="3.0">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:param name="input"/>
<xsl:variable name="newline" select="'
'"/>
<xsl:template match="/" name="xsl:initial-template">
<xsl:variable name="input-as-map" select="parse-json($input)" as="map(*)"/>
<root>
<file1>
<xsl:for-each select="$input-as-map?file1?*">
<xsl:value-of select="$newline"/>
<xsl:value-of select="concat(?emp_no,',',count(?emp_no))"/>
<xsl:value-of select="$newline"/>
</xsl:for-each>
</file1>
</root>
</xsl:template>
</xsl:stylesheet>
input json:-
{
"file1": [
{
"emp_no": "0002"
},
{
"emp_no": "0009"
},
{
"emp_no": "0002"
},
{
"emp_no": "0009"
},
{
"emp_no": "0009"
}
]
}
Expected output:-
<root>
<file1>
0002,1
0009,1
0002,2
0009,2
0009,3
</file1>
</root>
Any suggestions also would be helpful.

Answer 1

One solution would be to replace the xsl:for-each with xsl:iterate, maintaining a parameter value containing a map from emp_no to an integer counter.
Another would be to convert the array to XML and use xsl:number.
Or you could use fn:fold-left(), again maintaining a map from emp_no to an integer counter as you step through the array.
None of them particularly easy, I'm afraid: perhaps someone else has a better idea.

Answer 2

Here is Mike's third suggestion spelled out:
<file>
<xsl:value-of
select="fold-left(
parse-json($json)?file1?*,
map{},
function($am, $m) {
let $c := head($am)($m?emp_no),
$new-am := map:put(head($am), $m?emp_no, if (empty($c)) then 1 else $c + 1)
return ($new-am, tail($am), $m?emp_no || ',' || $new-am($m?emp_no))
}
) => tail()"
separator="
"/>
</file>